Just wanted to know which country or individual has the most DB medals?

Ross Flemer has been a member of USA's Premier Open and Premier Mixed for as long as there have been World Championships. That's a lot of medals right there and probably the most by a USA paddler. I don't know how that compares to long-time members of teams from other countries.

Just wanted to know which country or individual has the most DB medals?

For World Championships only (not club crews or World Cup) Flemer would have roughly 34 medals at the Premier level. That covers 12 Worlds from 97 to Kunming, he did not race in the First Worlds. No official 2K until 2007. Trial event in 2005. Philly paddlers did not get significantly involved in Mixed until 2004, a few raced in 2003 in Mixed to fill the boat out. Mixed teams were primarily out of Portland area before that. Doubt anyone matches that longevity at Premier level, probably not many with that medal count.